Cummins Offers Insight Into Reasons For Switch To SCR

May 1, 2009

LOUISVILLE, Ky. - When Cummins shocked the industry last August by announcing it was abandoning its plans to achieve EPA2010 compliance using an incylinder solution in favour of selective catalytic re...

May 1, 2009
by
James Menzies

Categories

LOUISVILLE, Ky. – When Cummins shocked the industry last August by announcing it was abandoning its plans to achieve EPA2010 compliance using an incylinder solution in favour of selective catalytic reduction (SCR), few reasons for the switch were provided.

At the time, Cummins officials said they were making the u-turn based on the discovery of a new copper zeolite catalyst material that made significant fuel economy improvements attainable using SCR, but it also said its incylinder solution was on-schedule and achievable.

At a press event at Louisville distributor Cummins Crosspoint preceding the Mid-America Trucking Show, the company revealed further details about why it had a sudden change of heart. The main reason for the switch remains the potential performance advantages of copper zeolite as a catalyst material, according to Steve Charlton, vice-president of heavy-duty engineering with Cummins. He explained the newly-discovered alternative has a NOx efficiency rate (the percentage of NOx removed by the catalyst) of more than 90%.That compares to an 85% conversion rate of traditional catalyst materials, he said, meaning the company will be able to program its engines for even greater performance and fuel economy.

Adding to copper zeolite’s appeal, Charlton explained the material maintains its performance at extremely high temperatures as well as at the bottom end of the temperature range. Suddenly, the advent of copper zeolite put SCR in a much more favourable light, according to Cummins.

Meanwhile, Charlton also revealed the company was facing considerable challenges in achieving its in-cylinder solution.

“The in-cylinder solution is definitely not without its challenges,” he said. “I believe we would have gotten there, but there were some stiff challenges.”

With EGR rates being ramped up from 25-30% in 2007 to about 45% for 2010, Charlton said Cummins struggled to maintain its current fuel consumption rates. He also pointed out that at such high volumes, the exhaust gas recirculated back into the cylinder contains water which runs the risk of condensing.

“Where does all this condensate go? It can go down past the piston ring and find its way into the cylinder,” he explained. He also noted the diesel particulate filter (DPF) was being overworked due to the high EGR rates, requiring more active regenerations and further hindering fuel economy.

Power density and torque were also being compromised during development of its in-cylinder solution, Charlton pointed out, necessitating the launch of a higher displacement engine. In fact, by adopting SCR, the company has abandoned plans to introduce a 16-litre ISX, since it can achieve the same performance with a 15-litre offering.

Charlton said Cummins found there was a 9% fuel economy swing between what it can achieve using SCR compared to what it was on pace to realize if it forged ahead with its in-cylinder solution. Even with a DEF penalty of about 2%, he said the fuel savings were too great to ignore, thus the decision was made to change paths.

Jim Kelly, president of Cummins engine business, added “We did make a bit of a right hand turn in August of last year…we felt that consistent with our commitment to our customer base in having the right technology in the right market at the right time, that we needed to make that change with the development of the copper zeolite material.”

He also addressed EPA concerns about the possibility copper zeolite could produce toxins, and was confident the EPA’s worries will be put to rest.

“We believe there’s no public harm associated with copper zeolite and we believe it will in fact be approved and be our technology going forward,” he said.